Lab series L11 low volume issue

[Klee]

I just picked up a lab series L11 head and cabinet for cheap.Very clean and in great physical condition.
Speakers are fine when driven by my fender twin but very weak and distorted sound when driven by the head. Happy to take it to a shop but thought I'd ask here first in case it's something simple like a fuse. I have no amp repair knowledge but love fixing things. Thanks

[jondoe]

A dead fuse normally means no output or no power on, so it's unlikely to be just a fuse.

[Klee]

Thanks!

[TomCarlos]

Something simple would also include cleaning the pots with Deoxit F5 cleaner/lube. You can find videos on YouTube showing how to do this. Here is one such video - Clean and Maintain Guitars, Amps, Pedals and More with Caig DeoxIT. Just make sure you use the F5 version for the final clean. F5 has a lubricant added.

[J M Fahey]

Agree and add: clean all pots, but also all jacks, switches, etc.

Specially on jacks which have weak leaf switches built in: squirt a little in, the tiniest amount possible, and insert/pull a plug 10/20 times so friction + cleaning fluid remove surface grime which cause poor contact and signal loss.

A great suspect is the loop send/receive pair, because unlike input jacks, it´s hardly used, so nothing stops grime from collecting.

[Klee]

I'm using a guitar cable to connect. Could this be the issue. I'm a newbie!

[Jazz P Bass]

Agree with JM.

Plug a guitar into the Power Amp In jack.
If the power amp now sounds good, then either the contacts in the jack are at fault or the preamp itself is.

Further testing: Send the Preamp Out to another amplifer.

[Jazz P Bass]

I'm using a guitar cable to connect. Could this be the issue. I'm a newbie!

To connect what?
The speaker?
The cable itself will not cause a crappy signal.
It simply cannot handle the wattage.

[TomCarlos]

Echoing JPB.... You need to get a speaker cable, something thicker, perhaps 16 gauge. If you are using an instrument cable to connect the speaker cab, that will limit the current flow and you will hear a lower volume level compared to using a thicker cable.

[Klee]

Thanks I'll give it a try

[Klee]

Still Sounds bad with guitar through 'power amp in' but good through 'preamp out'. (A big amp through to a small one, but not sure that matters)

[Klee]

Still Sounds bad with guitar through 'power amp in' but good through 'preamp out'. (A big amp through to a small one, but not sure that matters)

[Bloomfield]

That sounds promising. The guitar plugged straight into the 'power amp in' most likely has too little signal level. You could try something with a line-level output: ie. a tape deck, CD player, mixer etc., or use a pedal after the guitar to boost the level. That ought to give you a better picture of how it is responding.

[Jazz P Bass]

Still Sounds bad with guitar through 'power amp in' but good through 'preamp out'. (A big amp through to a small one, but not sure that matters)

If by "still sounds bad" you mean "very weak and distorted sound" (from Post #1) then you have a power amplifier problem.

" I have no amp repair knowledge but love fixing things".
In this case you may end up with a boat anchor if you are not careful.
This is by no means a 'simple' amplifier.

On top of that more than a few of the transistors will be hard to find.
In that case you may have to twist package leads to get the proper configuration.

Lab II.zip

[Klee]

Will do and thanks. This is all very interesting stuff